A torque converter that is mounted on an automatic transmission and transmits the engine output to the transmission includes, in a case coupled to an output shaft of the engine, a pump which rotates integrally with the case, a turbine disposed opposite to the pump and which is driven by the pump via a fluid, and a stator disposed on the inner side of a part between the pump and the turbine that are opposite to each other.
The stator is supported by a transmission case via a one-way clutch disposed on an inner side of the stator, and increases the torque by being fixed at an area where the velocity ratio is small; that is, area where the ratio of the turbine speed relative to the pump speed is small, and receiving the reactive force of the fluid that flows backward from the turbine to the pump.
A turbine shaft coupled to the turbine and extending toward the transmission is disposed on the center line of the torque converter. A stator shaft extending from the transmission case and fitted with the inner race of the one-way clutch is disposed on the outside of the turbine shaft. And further, a pump sleeve extending from the case of the torque converter toward the transmission to drive the oil pump serving as a fluid supply source is disposed on the outside of the stator shaft.
Moreover, a torque converter is sometimes provided with a lock-up clutch which directly couples the pump and the turbine in order to improve the fuel economy of the engine during the driving state excluding cases of starting the vehicle and the like in which the torque increasing effect by the stator is utilized, or of a gear-change which requires to allow the relative rotation of the pump and the turbine. As this lock-up clutch, a multiple-disc lock-up clutch including a piston which locks a plurality of friction plates when a predetermined working pressure is supplied to these friction plates and a hydraulic chamber.
With a torque converter including this kind of lock-up clutch, a fluid is introduced from the oil pump to the space between the stator shaft and the turbine shaft. The fluid is supplied to a torus configured from the pump, the turbine and the stator, and additionally supplied to the space where the lock-up clutch is disposed, and thereby fills the torque converter.
In addition to transmitting the torque in the torus, this fluid also functions to cool the heat that arises during the slip control of the lock-up clutch. The fluid that is heated as a result of transmitting the torque and cooling the lock-up clutch in the torque converter is discharged from the space between the pump sleeve and the stator shaft.
Nevertheless, there is a possibility that a part of the fluid that was introduced from the space between the stator shaft and the turbine shaft will leak from the space between the pump sleeve and the stator shaft through the spline engagement part of the inner race and the stator shaft of the one-way clutch without circulating through the torus and the space where the lock-up clutch is disposed, and it will not be possible to sufficiently cool the lock-up clutch.
Meanwhile, for example, the type disclosed in Japanese Patent Application Publication No. 2008-175338 is known to improve the cooling performance of the lock-up clutch. As shown in FIG. 6, in this torque converter 201, the turbine is coupled to the turbine shaft F11 of the automatic transmission at the position shown as P11. Specifically, the turbine hub 211 coupled to the turbine is coupled to the turbine shaft F11 via spline engagement.
Moreover, in this torque converter 201, the inner race 221 of the one-way clutch 220 is spline-engaged with the stator shaft F12 at the position shown as P12, and fitted tightly (that is, tightly engaged) with the stator shaft F12 at the position shown as P13 that is more on the non-engine side (that is, the side that is farther from the engine relative to the spline engagement part P12) than the spline engagement part P12 with the stator shaft F12.
In addition, in the torque converter 201, the fluid that is introduced from the space between the stator shaft F12 and the turbine shaft F11 is supplied to the space 240 where the lock-up clutch is disposed by passing through, as shown with the arrow A11, the fluid passage 231 provided to the stator shaft F12, the fluid passage 232 provided to the inner race 221, and the fluid passage 233 provided to the turbine hub 211, supplied from the space 240 to the torus configured from the pump, the turbine and the stator, and, as shown with the arrow A12, discharged from the torus to the space between the pump sleeve 216, which is coupled to the case 215, and the stator shaft F12.
Thus, this torque converter 201 improves the cooling performance of the lock-up clutch by spline-engaging and tightly fitting the inner race 221 and the stator shaft F12 and supplying the fluid, which was supplied from the space between the stator shaft F12 and the turbine shaft F11, to the space 240 where the lock-up clutch is disposed. Note that, with this torque converter 201, the fluid which controls the operation of the lock-up clutch is supplied through the fluid passage 241 extending in the axial direction of the turbine shaft F11 as shown with the arrow A13 separately from the fluid passages shown with the arrows A11 and A12.
Nevertheless, even in cases of inhibiting the leakage of the fluid to the space between the pump sleeve and the stator shaft through the space between the inner race and the stator shaft by providing a tightly fitted part (that is, a portion that is tightly engaged) on the non-engine side of the spline engagement part of the inner race and the stator shaft as described in foregoing Japanese Patent Application Publication No. 2008-175338, in actually, when considering the assemblability of the inner race housed in the torque converter and the stator shaft extending from the transmission case, it is necessary to provide a clearance between the inner race and the stator shaft at the tightly fitted part.
If a clearance is provided between the inner race and the stator shaft at the tightly fitted part, as described above, the fluid will leak to the space between the pump sleeve and the stator shaft through the space between the inner race and the stator shaft, and the lock-up clutch cannot be sufficiently cooled.